Define the version number in just one place

[tesujimath]

Version appears to be defined in several places, and they are inconsistent.

• GBS-Chip-Gmatrix.R has KGDver <- "1.3.1"
• GBS-PopGen.R has PopGenver <- "1.3.1"
• GBSPedAssign.R has pedver <- "1.3.0"
• flake.nix has version = "1.2.2"

and in addition there is the git tag.

Most practical solution is to create a text file called VERSION which contains just the version string, and have everything else read this. In Nix you can do that with version = builtins.readFile ./VERSION. Although this may not be that straightforward given the lack of R packaging for this project. Deployment is a real issue because its not packaged on CRAN. 😢

(And check it works afterwards by running nix build)

Note that Nix can't read the git tags (because .git is not available to Nix derivations for good reasons), so no point trying to be clever and derive the version from the git tags.